<em># 声明焦点事件</em>
<em>FocusNode</em> <s>focusNode</s> = <em>new</em> <q>FocusNode( )</q>;

<em>Future&lt;Null&gt;</em> <s>_focusNodeListener</s>( ) <b>async</b> {
	if (<s>focusNode</s>.<i>hasFocus</i>){
		<em>// 得到焦点</em>
	} else {
		<em>// 失去焦点</em>
	}
}

<em># 监听焦点事件</em>
<u>@override</u>
<em>void</em> <u>initState( )</u> {
	super.<u>initState()</i>;
	<s>focusNode</s>.<b>addListener</b>(<s>_focusNodeListener</s>);
}

<em># 移出焦点事件</em>
<u>@override</u>
<em>void</em> <u>dispose( )</u> {
	super.<u>dispose()</i>;
	<s>focusNode</s>.<b>removeListener</b>(<s>_focusNodeListener</s>);
}

<em># 使用</em>
<u>C</u>(
	<i>focusNode</i> : <s>focusNode</s>
)